not sure what your thinking here so just trying to help...most of the time when i read this statement people (jetting down) they think there taking over carbing a engine away. in reality cfm is not effected putting smaller jets in any carb, only changes the air fuel ratio. typically when a carb is to big for the app or on the large side anyway they run towards the lean side. during lower rpm and on the transition. this is usually fixed buy working with the air bleeds in the carb not the jets. although jets may need to be changed to get the carb right. most carb are built with jets that are very close to right and that would include this situation. most holley 390s are vacuum secondaries and that perfect for a slant cause they wont open till the engine is pulling nubers to open it. just so you know ive put them on toyota 22r engine and had it work great so a slant is even larger and better size wise. hope this helps i say do it
